In current wireless communications systems, 5 MHz˜10 MHz radio bandwidths are typically used for up to 100 Mbps peak transmission rate. Much higher peak transmission rate is required for next generation wireless systems. For example, 1 Gbps peak transmission rate is required by ITU-R for IMT-Advanced systems such as the 4th generation (“4G”) mobile communications systems. The current transmission technologies, however, are very difficult to perform 100 bps/Hz transmission spectrum efficiency. In the foreseeable next few years, only up to 15 bps/Hz transmission spectrum efficiency can be anticipated. Therefore, much wider radio bandwidths (i.e., at least 40 MHz) will be necessary for next generation wireless communications systems to achieve 1 Gbps peak transmission rate.
Orthogonal Frequency Division Multiplexing (OFDM) is an efficient multiplexing scheme to perform high transmission rate over frequency selective channel without the disturbance from inter-carrier interference. There are two typical architectures to utilize much wider radio bandwidth for OFDM system. In a traditional OFDM system, a single radio frequency (RF) carrier is used to carry one wideband radio signal, and in an OFDM multi-carrier system, multiple RF carriers are used to carry multiple narrower band radio signals. An OFDM multi-carrier system has various advantages as compared to a traditional OFDM system such as easier backward compatibility, better reuse on legacy single-carrier hardware design, more mobile station hardware flexibility, and lower Peak to Average Power Ratio (PAPR) for uplink transmission. Thus, OFDM multi-carrier systems have become the baseline system architecture in IEEE 802.16m and 3GPP LTE-Advanced draft standards to fulfill system requirements.
FIG. 1 (Prior Art) illustrates a typical architecture to utilize much wider radio bandwidth for OFDM multi-carrier system 11. In OFDM multi-carrier system 11, multiple RF carriers are used to carry multiple radio signals with narrower bandwidth (called narrower band radio signal). In the example of FIG. 1, the total radio bandwidth of OFDM multi-carrier system 11 is 40 MHz, and four RF carriers #1-#4 are used to carry four narrower band radio signals #1-#4, each transmitted through a corresponding 10 MHz frequency channel #1-#4 (i.e., 10 MHz Bandwidth, 1024 FFT). For each RF carrier, the overall radio bandwidth is further partitioned into a large number of sub-carriers, which are closely spaced and orthogonal to each other for data transmission. When there are contiguous frequency channels used for data transmission, sub-carriers in between adjacent frequency channels may be overlap with each other. Therefore, overlapping sub-carriers located in between adjacent frequency channels are typically reserved as guard sub-carriers to prevent signal interference.
As illustrated in FIG. 1, at both end of each frequency channel, a certain number of sub-carriers are reserved as NULL sub-carriers such that they are not used for data transmission. However, if both adjacent frequency channels are controlled and managed by the same base station, then it is not necessary to have those overlapping sub-carriers in between adjacent frequency channels to be reserved as guard sub-carriers. Instead, the guard sub-carriers in between adjacent frequency channels may be used for data transmission such that overall system throughput can be increased. For example, in IEEE 802.16m wireless communications systems, allowing data transmission over guard sub-carriers can increase system throughput by 2.08% for two contiguous 10 MHz frequency channels, by 2.77% for three contiguous 10 MHz frequency channels, and by 3.125% for four contiguous 10 MHz frequency channels. It is thus desirable to enable data transmission over guard sub-carriers to increase overall system throughput and peak transmission rate.